1. Field of the Invention
The invention relates to a compressor for gas turbines, and in particular to a coating for protecting against liquid drops and solid particles, which is applied to the surfaces of components in the inlet region of the compressor.
2. Brief Description of the Related Art
The components of compressors in turbines, such as for example power plants, aircraft and ship engines, are exposed to various particles during compressor operation, which may cause permanent damage to the surfaces of the components. These particles include liquid drops, inter alia water drops, and solid particles, such as for example dust particles, which enter the compressor together with the intake air. Mention should also be made of ice particles, which may form through desublimation as a result of the cooling of the air caused by the acceleration of the air. Of the components in the inlet region of the compressors, in particular the blading is affected by potential damage from these particles.
It is known that, during compressor operation, certain liquids are deliberately injected with the gas or air stream. For example, for cleaning purposes a mixture of water and a commercially available concentrate is injected into the compressor by means of one or more atomization nozzles, as described, for example, in EP 0 468 024.
During winter operation, the formation of ice at the entry to the compressor blading and the intake of ice particles (also known as ice ingestion) is extremely harmful to the integrity of the compressor. For this reason, glycol mixtures are injected to prevent the formation of ice at the compressor inlet.
Furthermore, water is introduced into the compressor by injection or atomization for the purpose of evaporative cooling of the intake gas or intake air. This evaporative cooling serves to increase the efficiency of the compressor and ultimately to increase the gas turbine power. A method of this type is disclosed, for example, by U.S. Pat. No. 5,463,873.
In the compressors of turbine jet engines, such as for example in aircraft and ships operated with gas turbines, the problem of damage to the compressor components arises, caused by rain, fog, mist, ice or salt water being sucked in.
If various liquids are injected or if liquid drops or solid particles are sucked in, the problem arises of drop impingement erosion or erosion caused by solid particles at the surfaces of the components, in particular of the blading and of the components in the inlet region of the compressor. Drop impingement erosion is caused, firstly, directly by the drops of liquid which are sprayed or sucked in on the surfaces of the components. At the start of the operating time of the spray nozzles for the injection of liquids, the drops which are sprayed in are initially small, i.e. with a diameter in the range from 10–20 micrometers. After a certain operating time, however, the spray nozzles become worn away such that the drops which they spray gradually reach a size of up to 100 micrometers in diameter. Since the mass and therefore the kinetic energy of the drops increases to the third power of the drop diameter, larger drops can cause far more erosion damage than small drops. Therefore, the drops which are sprayed by the spray nozzles may cause considerable drop impingement erosion.
Secondly, drop impingement erosion also occurs after the formation of continuous films of liquid if the components have been wetted by the injected liquid. The detachment of liquid from a surface allows secondary large drops to form, which can cause drop impingement erosion on components arranged downstream.
Finally, there is also the general problem of contamination caused by constituents which have been added to the injected water and gradually build up on the surfaces. Deposits of these constituents and of further foreign material may have an adverse effect on the service life of the components and also on the power of the gas turbine.